All depends on what your after mate? What do you want your car to be doing? Weight wise 1.8T and vr6 are about the same.
The mk3 VR6 are not really powerful engines and power wise they cannot have alot more done to them, all you can do is uprate your cams and lighten your flywheel to see a better overall response and gain. Otherwise spend huge money for a turbo conversion...
The 1.8T engines are not that much powerful (the early specs, such as AGU) but they will push 200bhp with 210lb torque with a remap (but the torque will be a fair bit more over the vr6), later engines like S3 and LCR 1.8T's remap to the 260bhp mark. Which is a considerable amount more off power, plus you will have all that extra pulling power due to the torque figures.
Its all down to what you want to be pushing, which is what you should really think about now before wasting additional money and then changing your mind.
Since your not to far from me, let me know when your free and I can show you what a 1.8T feels like and maybe consider if its something you may or may not want, unfortunately the mk4 weighs as much as an elephant and is not as light as your mk3.
